The present invention relates to testing apparatus, and more particularly to means for inspecting cylindrical metal containers for structural integrity and for the presence of an internal coating.
The manufacture of metallic containers, and particularly steel or aluminum cans of the one-piece drawn and ironed type, places severe demands upon the manufacturing process. On one hand, it is necessary to be able to manufacture the containers in substantial quantities and therefore at a high rate. On the other hand, it is necessary that each container be structurally sound so that it may be properly filled and sealed, and it is also highly desirable that each container be labelled, coated, and otherwise treated in a prescribed fashion. In particular it is necessary that certain types of containers, depending upon the use to which they are to be put and the substances which they are to contain, have a coating applied thereto so as not to impart an undesirable taste to the contents.
With the advent of drawn and ironed containers the criticality of the manufacturing process has become even more demanding. Such containers are initially drawn from sheet metal blanks, then forced through a series of annular dies of progressively decreasing diameter so as to form a one-piece can body having extremely thin walls. Due to the necessity of handling the cans in high volume and thus at relatively high flow rates, the cans are occasionally dented or otherwise damaged. Further, during the formation of the outer flanges thereof the thin sidewall metal occasionally cracks. Although it is apparent that the defects so far described must be detected during the can manufacturing process, satisfactory means for rapidly and economically effecting such inspection do not exist in the prior art.
A further problem with prior manufacturing processes is the facile detection of substantial uncoated areas within a container. Modern coating apparatus ordinarily produce an acceptably uniform coating over the ends and sidewalls of containers. However, occasionally the apparatus, which conventionally takes the form of a plurality of spray nozzles, becomes clogged and inoperative. In such a case the sidewalls, end walls, or both remain uncoated. Since the coating is ordinarily a transparent lacquer-like material the absence of the coating is not immediately apparent and not infrequently a large number of containers will pass uncoated before the failure is detected.
It will therefore be understood that it would be highly desirable to provide improved means for rapidly inspecting certain aspects of the structural integrity of a metallic container, and for rapidly and accurately testing for the presence of a coating upon the inner surfaces of the container.
It is therefore an object of the present invention to provide improved means for checking the structural integrity of a metallic container.
It is another object of the present invention to detect minute splits in the flange area of a metallic container.
Another object of the invention is to detect predetermined eccentricity in the sidewalls of a cylindrical metallic container.
Still another object of the present invention is to automatically detect the absence of coating material on the lateral or end surfaces of a metallic container.